The present invention relates to a body fluid sampler for sampling blood for example for measuring the glucose concentration in the blood (hereinafter referred to as xe2x80x9cblood sugar levelxe2x80x9d) for example.
For the treatment of diabetes, it is necessary to maintain the blood sugar level to a normal range. Particularly for the treatment of insulin-dependent diabetes mellitus, a patient needs to conduct insulin injection by himself or herself to keep the blood sugar level to a normal range. In this case, the patient needs to appropriately check the blood sugar level to determine whether the blood sugar level is within the normal range.
Generally, for sampling blood to measure the blood sugar level, use may be made of a portable blood sampler which internally holds, at the tip end of the apparatus, a piercing needle called lancet. In using such a blood sampler, the skin of the patient is instantaneously stabbed by the pointed tip of the lancet. The patient causes the blood sampler to draw blood from the stabbed portion and applies the sampled blood to a blood test piece. In this way, the determination of the blood sugar level can be performed relatively easily.
Such a prior art blood sampler is disclosed in JP-A-5-95937 or JP-A-10-127610 for example. In the prior art sampler disclosed in the former publication, while the tip end of an apparatus body is pressed against the skin of a forearm, a push member is pushed down by a thumb against the repulsive force of a coil spring, thereby stabbing the pointed tip of a lancet into the skin under magnetic action. Thereafter, by retreating the pressing member together with the lancet, the pointed tip of the lancet is removed from the skin. At this time, the air in the interior of the apparatus body undergoes a pressure reduction to cause the stabbed portion to bulge for prompting blood bleeding from the portion stabbed by the lancet.
The prior art sampler disclosed in the latter publication solely utilizes the repulsive force of a spring for pushing down a push member provided at the upper end of an apparatus body to stab the skin with a lancet followed by skin bulging. In use, specifically, the push member provided at the upper end is first pulled up to make the apparatus ready for use. Then, with the tip end of the apparatus pressed against the skin of a forearm for example, the push member is pushed down by a thumb. As a result, the air within the apparatus body escapes to the outside through a non-return valve. When the push member is further depressed, the pointed tip of the lancet stabs the skin. By subsequently removing the thumb from the push member, the force of the spring causes the push member to move back upward. At this time, the interior of the apparatus body undergoes a pressure drop, causing the stabbed portion to bulge. Finally, the push member is pushed down again to relieve the vacuum state within the apparatus body back to the atmospheric pressure, consequently allowing the tip end of the apparatus body to be removed from the skin.
However, the above-described blood samplers have the following drawbacks.
In the prior art sampler disclosed in the former publication, the push member is depressed by one thumb with the tip end of the apparatus body pressed against the skin. In this prior art sampler, however, the air trapped in the apparatus body is compressed, so that a considerable power is required to push down the push member. Moreover, the push member need be pushed down by a considerable stroke. Therefore, the handling of the apparatus by one hand is extremely difficult for a patient having an insufficient force. Further, in depressing the push member with the tip end of the apparatus body pressed against the skin, the patient may fear that the pointed tip of the lancet stabs deeply in the skin particularly when the stroke of the push member is long. Moreover, since the prior art sampler is not provided with means for relieving the vacuum in the apparatus body, blood may splash in removing the pointed tip of the apparatus body from the skin.
Since the prior art sampler disclosed in the latter publication also samples blood only by the operation of the push member, it has the same drawbacks as those of the foregoing prior art sampler. Particularly in this prior art apparatus, the push member need be depressed again to relieve the vacuum state within the apparatus. Therefore, there is a possibility that the lancet stabs the skin again when the push member is excessively depressed.
It is therefore an object of the present invention to provide a body fluid sampler which is capable of eliminating or at least lessening the above-described problems.
According to the present invention, there is provided a body fluid sampler comprising a cylindrical main case having a first end provided with a first opening and a second end provided with a second opening, a piston inserted in the main case to project from the first opening for movement within the main case airtightly with respect to an inner wall of the main case, a first plunger rod extending integrally from the piston toward said second end, a first elastic member for elastically urging the piston toward said first end, a second plunger rod extending from the first plunger rod toward said second end for movement within the main case with a compressible second elastic member interposed between the first plunger rod and the second plunger rod, a lancet mount associated with the second plunger rod adjacent to said second end for movement within the main case, the lancet mount being provided with a lancet oriented toward said second end, third elastic member for elastically urging the lancet mount toward said first end, latch mechanism which works, when the piston is pushed down for movement toward said second end together with the first plunger rod, for restricting movement of the second plunger rod toward said second end against a pushing force of the second elastic member and for restricting rebounding of the piston and first plunger rod which have been moved toward said second end while allowing the second elastic member to be compressed, and a release mechanism for releasing the first plunger rod and second plunger rod which have been latched by the latch mechanism.
Specifically, the latch mechanism includes a first and a second engagement members each of which has a stopper for stopping a corresponding one of the first and the second plunger rods, a latching elastic member for elastically biasing each of the engagement members toward the corresponding one of the first and the second plunger rods, and engagement portions respectively formed on the first and the second plunger rods, the engagement portions being spaced from each other by a distance which is larger than a distance between the stoppers when the plunger rods are held in an initial state, the release mechanism including a release button for simultaneously releasing the stoppers from the corresponding engagement portions against an elastic biasing force of the latching elastic member.
In the above-described body fluid sampler, the piston moves toward the second end of the main case when it is depressed by the user. As a result, the second elastic member is elastically compressed between the first and the second plunger rods, thereby storing an elastic restoring force. The engagement portion of the first plunger rod engages the stopper of the first engagement member with the first plunger rod biased toward the first end by the second elastic member. The engagement portion of the second plunger rod engages the stopper of the second engagement member with the second plunger rod biased toward the second end by the second elastic member. In this way, the both plunger rods are restricted.
Subsequently, the user pushes the release button of the release mechanism with the second opening of the main case pressed against the skin. When the release button is pushed, the second plunger rod hits or pushes the lancet mount downward due to the elastic force of the second elastic member. Thus, the pointed tip of the lancet instantaneously stabs the skin facing the second opening of the main case. The first plunger rod and the piston return to respective positions before the operation due to the elastic restoring force of the second elastic member and the first elastic member. As a result, the interior of the main case undergoes a pressure reduction to cause the stabbed portion to bulge for prompting blood bleeding from the stabbed portion.
In this way, according to the above-described body fluid sampling apparatus, the preparation for launching the lancet B can be completed by depressing the piston before bringing the second end of the main case into pressing contact with the skin. Since the interior of the main case is held at the atmospheric pressure at this time, even a patient having an insufficient force can conduct the operation by one hand. Moreover, the stroke for depressing the piston is not so long, the user can handle the body fluid sampler easily without anxiety.
According to a preferred embodiment of the present invention, the release button is provided with a push portion projecting from a predetermined portion of a side surface of the main case while keeping airtightness relative to the main case.
With this structure, even when the release button is operated, the airtightness of the main case is maintained. Therefore, just by once pushing the release button, the stabbing of the skin by the lancet and the pressure reduction in the main case can be carried out instantaneously and easily without causing pain to the patient.
According to a preferred embodiment of the present invention, the main case may be provided with a vacuum relief mechanism for relieving a vacuum state within the main case generated by pulling back the piston toward said first end.
Preferably, the vacuum relief mechanism may be provided with a vacuum relief button partially projecting from a predetermined portion of a side surface of the main case, the vacuum relief button being elastically urged in the projecting direction while keeping airtightness of the main case, the vacuum relief button being pushed against the elastic urging force for allowing air passage between inside and outside of the main case.
With this structure, after the stabbing of the skin by the lancet and the pressure reduction in the main case are completed, the pressure in the main case can be returned to the initial atmospheric pressure just by once operating the vacuum relief button. Thus, the second end of the main case formed with the second opening can be easily removed from the skin.
According to a preferred embodiment of the present invention, the piston has an outer circumferential wall provided with an O-ring for closely contacting the inner wall of the main case.
With this structure, the airtightness between the piston and the main case is sufficiently maintained by the O-ring. Therefore, the pressure within the main case can be sufficiently reduced by pulling up the piston to the initial position.
Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings.